Perforating apparatus



Feb; 25, 1969 J. B. SHORE 3,429,384

PERFORATING APPARATUS Filed oCt- 9, 1967 Ja'me: .5. J/zore INVENTOR.

United States Patent 3,429,384 PERFORATING APPARATUS James B. Shore,Friendswood, Tex., assignor to Schlumberger Technology Corporation,Houston, Tex., a corporation of Texas Filed Oct. 9, 1967, Ser. N0.673,665 US. Cl. 175--4.6 Int. Cl. E21b 43/116; E21c 19/00 8 ClaimsABSTRACT OF THE DISCLOSURE Accordingly, as will subsequently becomeapparent, the present invention pertains to perforating apparatus. Moreparticularly, the present invention relates to new and improved shapedcharge perforating apparatus and to methods for producing suchapparatus, which apparatus includes an expendable-type, enclosedretrievable carrier that is particularly adapted for service in wellshaving one or more strings of small-diameter tubing through which theperforating apparatus must pass.

To complete many wells today, the borehole is typically cased and asmall-diameter tubing string extended through a conventional packer setjust above the uppermost producing zone therein. Where two or moreproductive intervals are to be completed in a particular well, packersare set above each of the producing zones, with a separatesmall-diameter tubing string being extended to each of these packed-offintervals for communication therewith. Thus, to perforate a well borehaving one or more productive intervals completed in this manner, theperforating apparatus must be passed through a smalldiameter tubingstring and then lowered below the lower open end of that tubing string.After emerging from the tubing string, the perforating apparatus isbrought into position and actuated to perforate the casing and cementand establish communication with that particular formation intervaladjacent thereto.

Where the perforating apparatus is of the so-called enclosed carriertype, it is, of course, essential that the carrier be appropriatelyarranged for reliable recovery through the open lower end of a tubingstring. In accordance with this requirement, shape charge perforatingapparatus as shown in Patent No. 3,048,102 has been recognized for manyyears as being a highly successful perforator that can be reliablyretrieved from wells as just described. As fully explained in thispatent, a small recess or concavity is formed in the outer wall of anenclosed tubular carrier immediately in front of each shaped chargetherein where, upon their detonation, the resulting perforating jet fromeach shaped charge will pass through the carrier wall at one of theseindentations. In this manner, at least a substantial portion of theirregular outward protrusion or so-called burr that is typically formedaround the place where each perforating jet exits from the carrier willlie within the circumferential bounds defined by the external diameterof the carrier. Thus, when the expended carrier is recovered, it willeasily pass through even a close clearance without being stuck 3,429,384Patented Feb. 25, 1969 as might otherwise occur should the burrsprotrude too far beyond the outer wall of the carrier.

It is, of course, recognized that the distance that a perforating jetcan travel as it is being formed before meeting an obstruction willsignificantly affect the performance of a shaped charge. In general,therefore, for a given shaped charge, its penetrating capability willincrease in direct relation to the length of this free travel orso-called stand-off distance until an optimum penetration depth isreached at a particular stand-off distance. Those skilled in the artwill appreciate, however, that where the largest possible shaped chargeis confined with in a given size of a tubular carrier such as that shownin Patent No. 3,048,102, the resulting stand-off distance is well belowthe optimum stand-off distance for that shaped charge.

Accordingly, it is an object of the present invention to provide new andimproved shaped charge perforating apparatus including an enclosedexpendable carrier which provides an increased stand-off distance forthe shaped charges therein while still preventing the expended carrierfrom becoming stuck by outwardly projecting burrs and the like formedupon detonation of the shaped charges.

It is a further object of the present invention to provide methods forfabricating a new and improved expendable shaped charge carrier.

These and other objects of the present invention are obtained by forminga recess or concavity in the outer wall surface of a tubular carrierimmediately in front of the intended location of each shaped chargetherein with a small outwardly-projecting dimple extending from withinthe concavity to about the circumferential bounds defined by the outsidewall diameter of the carrier. In this manner, a significant increase inavailable stand-01f distance is provided while still minimizingundesirable projectons of burrs formed upon detonation of the shapedcharges in the carrier.

The novel features of the present invention are set forth withparticularity in the appended claims. The operation, together withfurther objects and advantages thereof, may best be understod by way ofillustration and example of certain embodiments when taken inconjunction with the accompanying drawings, in which:

FIGURE 1 shows perforating apparatus arranged in accordance with theprinciples of the present invention as it is being positioned in atypical well bore;

FIGURE 2 is a transverse cross-sectional view of the perforator shown inFIGURE 1;

FIGURE 3 is a partial elevational cross-sectional view of the perforatordepicted in FIGURE 2 as it might appear after detonation 0f the shapedcharges contained therein; and

FIGURES 4 and 5 are partial elevational views illustrating one manner offorming the perforator illustrated in FIGURES 1-3.

Turning now to FIGURE 1, perforating apparatus 10 is shown as it isbeing positioned in a typical cased well bore 11 adjacent to aproducible earth formation 12. As is customary, a small-diameter stringof tubing 13 is suspended in the well bore 11 and extended through atypical packer 14 set therein above the earth formation 12. If,perchance, the well bore 11 traverses another producible formation (notshown) below the formation 12, a second tubing string 15 is alsoextended through the packer 14 to the lower zone and packed-off there bya similar packer (not shown) so as to isolate the two producing zonesfrom one another and from that portion of the well bore above the upperpacker.

The perforating apparatus 10 issuspended in the usual manner from asuitable cable 16 that is spooled from a winch (not shown) at thesurface and connected to a cable head 17 on the upper end of theperforating apparatus. A typical casing collar locator 18 is employedfor providing indications at the surface representative of the depth ofthe perforating apparatus 10. To insure that the perforating apparatusis correctly positioned, a positioning device 19 such as that shown inPatent No. 3,338,- 317 is connected between the collar locator 18 and aperforator 20 arranged in accordance with the present invention. It willbe appreciated, of course, that other positioning devices such as thatshown in Patent No. 3,110,257 could just as well be employed if suchpositioning devices are ever needed.

Turning now to FIGURE 2, an enlarged transverse cross-sectional view isshown of the perforator 20 to illustrate the present invention. Theperforator 20 includes a fiuid-tight, elongated tubular carrier 21having upper and lower closure members and in which perforating meansincluding a plurality of laterally directed shaped charges 22 (only oneshown) are supported by an elongated plate 23 extending parallel to thelongitudinal axis of the carrier and having longitudinally spacedapertures 24 therein for receiving the shaped charges. As is customary,the perforating means include a detonating cord 25 that is extendedthrough the carrier 21 and maintained in operative relation to theshaped charge 22 as by an external groove 26 formed in the rear of eachshaped charge. The detonating cord 25 is, of course, coupled to aconventional detonator (not shown) in the carrier 21 that iselectrically connected by way of the suspension cable 16 to a suitablepower source (not shown) at the surface.

As fully described in Patent No. 3,048,102, the materials employed aswell as the particular dimensional relationships of the carrier 21 will,of course, be determined by the well bore pressures to be expected aswell as by the quantity of explosives contained in the shaped charges22. In general, therefore, the same parameters defined in Patent No.3048,102 will be applicable to carriers, as at 21, embodying the presentinvention.

In accordance with the present invention, that portion of the wall ofthe carrier 21 immediately in front of each shaped charge 22 isappropriately machined in a concavoconvex fashion to provide anoutwardly-directed protrusion or dimple 27 having a wall thickness lessthan that of the other portions of the carrier, with this dimple beingcompletely confined within an inwardly-directed concavity 28 formed inthe external wall of the carrier. As shown in FIGURE 2, by forming thedimple 27 within the concavity 28, the forward surface of the dimpledoes not extend beyond the bounds defined by the outer circumference ofthe carrier 21. Thus, the dimples 27 will in no way hamper the passageof the carrier 21 through a tubing string as at 13.

Of even greater significance, it will be appreciated from FIGURE 2 thatby forming each of the dimples 27 uniformly about the perforating axis29 of their respectively associated shaped charge 22, theoutwardly-directed concavity or recess 30 inside of each dimple willresult in a substantial increase in the stand-oft" distance between theshaped charge and the interior Wall of the carrier 21. Although theactual distance gained may be only a fraction of an inch, those skilledin the art will appreciate that even such a slight dimensional increasewill provide a significant increase in the depth to which the resultingperforating jet will penetrate a given target. For example, comparativetests conducted in accordance with standard A.P.I. RP-43 procedures haveshown that, with all else being equal, the perforator 19 as shown inFIG- URE 2 produced perforations that were in the order of to deeperthan the perforations obtained withperforators arranged as shown inPatent No. 3,048,102. It will be appreciated, therefore, that suchincreased penetration depths are of significance to the industry.

Turning now to FIGURE 3, an elevational view in cross section is shownof a portion of the carrier 21 after the shaped charges 22 have beendetonated. It will be noted that although an outwardly projecting burr31 is formed in the central portion of the dimple 27, little or none ofthis burr will extend beyond the bounds defined by the outercircumference of the carrier 21. Moreover, by virtue of the externalconcavity 28 and the reduced thickness of the dimple 27, even if someportion of the burr 31 were to protrude beyond the diameter of thecarrier 21, these protruding portions would be so weak that they wouldnot hamper the return of the carrier through a tubing string such as at13. It will also be noted in FIG- URE 3 that some swelling, as at 32,will be experienced in the Walls of the carrier 21 in the vicinity ofeach shaped charge 22. Hereagain, however, as discussed in Patent No.3,048,102, the degree of this swelling can be regulated as deemednecessary.

It will be recognized, of course, that the dimples 27 and recesses 28can be formed in several different manners. It has been foundparticularly economical, however, to form the dimples 27 and recesses 28as shown in FIGURES 4 and 5. Accordingly, as seen in FIGURE 4, thecarrier 21 is initially formed in accordance with the teachings ofPatent No. 3,048,102, with a scalloped-out concavity 28 being machinedin the external surface immediately in front of where each of the shapedcharges 22 are to be located. In the preferred embodiment of the presentinvention, the surface of each concavity 28 can be defined as being theintersection of an imaginary cylinder at right angles to the carrier 21,with this imaginary cylinder being of about the same or a slightlysmaller diameter as the carrier and having a longitudinal axis thatperpendicularly intersects the perforating axis 29 at a pointsufficiently in front of the carrier as to leave a minimum wallthickness at least adequate to withstand anticipated well borepressures.

Once the concavities 2 8 are formed, a hydraulicallyactuated formingtool 33 is inserted into the interior of the carrier 21. As shown inFIGURE 4, this forming tool 33 preferably includes a piston 34 having ahemisphericallyshaped forward head portion of forming mandrel 35, withthe piston being slidably received in a lateral bore 36 in a cylindricalbody 37. O-rings 38 or the like fluidly seal the piston 34 in the bore36 and provide an enclosed chamber 39 in the body 37 at the rear of thepiston which is in communication with a pressure source (not shown) byway of a suitable conduit such as a pipe 40. A stop shoulder 41 isarranged on the piston 34 to engage an opposed shoulder 42 on the toolbody 37 and limit the forward travel of the piston.

Accordingly, by positioning the forming tool 33 within the carrier 21 sothat the longitudinal axis of the piston 34 is coincidentally alignedwith the perforating axis 29 intersecting the concavity 28 and thenapplying a substantial hydraulic pressure to the chamber 39, thehemispherical head 35 will produce the complementarilyshaped dimple 27as shown in FIGURE 5 which circumscribes the perforating axis, with asubstantial portion of the dimple having a uniform radius of curvature.It will be appreciated, moreover, that either the forming tool 33 can besuccessively positioned adjacent to each recess 28 in turn or a formingtool (not shown) having a plurality of forming mandrels similar to thatat 35 can be employed.

It will be recognized, therefore, that the present invention hasprovided a new and improved perforator which, in service, will producesubstantially deeper perforations than can be obtained with comparableperforations known heretofore. Moreover, by forming the perforator inaccordance with the methods set out above, protruding burrs that mightotherwise cause the perforator to become stuck whenever it is to beretrieved are eliminated or at least minimized.

While a particular embodiment of the present invention has been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects; and,therefore, the

aim in the appended claims is to cover all such changes andmodifications as 'fall within the true spirit and scope of thisinvention.

What is claimed is:

=1. Perforating apparatus comprising: a tubular carrier adapted forpassage through a Well bore and having in an outer wall surface thereofa recess defining an integral wall portion of reduced thickness inrelation to adjacent 'Wall portions therearound, said reduced-thicknessWall portion including a smaller central portion thereof projectingoutwardly from within said recess to about the bounds defined by saidouter wall surface of said adjacent wall portions and defining anoutwardly-directed concavity in the inner wall surface of said centralportion; and perforating means in said carrier including a shaped chargemounted therein and facing said concavity with the perforating axis ofsaid shaped charge intersecting said concavity.

2. Th perforating apparatus of claim 1 wherein: said carrier iscylindrical and said recess defines an integral wall portion of varyingthickness uniformly decreasing from a maximum thickness above and belowsaid rec ss to a minimum reduced thickness in the center of said smallercentral portion; and said perforating axis intersects said concavitysubstantially at said center of said smaller central portion.

3. The perforating apparatus of claim 1 wherein: a major portion of saidinner wall surface of said concavity has a substantially uniform radiusof curvature.

4. The perforating apparatus of claim 3 wherein: said carrier iscylindrical and said recess defines an integral wall portion of varyingthickness uniformly decreasing from a maximum thickness above and belowsaid recess to a minimum reduced thickness in the center of said smallercentral portion; and said perforation axis intersects said concavitysubstantially at said center of said smaller central portion.

5. A perforating carrier comprising: an elongated tubular cylindricalbody of substantially uniform wall thickness and having a plurality ofinwardly-directed concavities at longitudinally-spaced intervals alongthe outer wall surface thereof, each of said inwardly-directedconcavities defining an integral wall portion of reduced thickness andencompassing an outwardly-directed dimple projecting therefrom to aboutthe circumferential bounds defined by said outer wall surface, and eachof said dimples having an inner wall surface defining anoutwardlyextending concavity.

6 -6. Perforating apparatus comprising: an elongated tubular cylindricalbody of substantially uniform wall thickness and having a plurality ofinwardly-directed concavities at longitudinally-spaced intervals alongthe outer of said dimples having an inner wall surface defining anoutwardly-extending concavity; perforating means in said carrierincluding a plurality of shaped charges mounted at longitudinally-spacedintervals therein and respectively facing said outwardly-extendingconcavities with their respective perforating axes intersecting saiddimples; and

means adapted for fluidly sealing said perforating means Within saidcarrier.

7. A perforating carrier comprising: a tubular cylindrical memberadapted for passage through a well bore and having internal and externalwall surfaces defining an integral wall of a uniform thickness, saidmember having at least one concavo-convex wall portion of a reducedthickness defining an outwardly-directed protrusion forming anoutwardly-directed recess in said internal wall surface and extendingoutwardly from within an inwardlydirected recess in said external wallsurface to a termination within the circumfer ntial bounds of saidexternal wall surface so that a shaped charge disposed within saidmember and facing said outwardly-directed recess will, upon detonation,perforate said reduced-thickness wall portion at said termination ofsaid protrusion, said inwardly-directed recess serving to effectivelycontain any significant burr resulting from such perforation within saidcircumferential bounds defined by said external wall surface.

8. The perforating carrier further comprising: perforating meansincluding a shaped charge mounted within said member adjacent to saidreduced-thickness wall portion and facing said outwardly-directed recesstherein.

References Cited UNITED STATES PATENTS 2,734,456 2/1956 Swe'etman 4.63,128,702 4/1964 Christopher 1754.6 3,190,219 6/1965 Venghiattis 1022.0

DAVID H. BROWN, Primary Examiner.

